Grease composition

ABSTRACT

Provided is a lubricating grease used for lubricating mechanical elements having a reciprocating sliding ball interposed therebetween and maintaining flaking resistance even under a high load in mechanical elements having a reciprocating sliding ball interposed therebetween. The present invention therefore provides a grease composition comprising a base oil (a), a diurea compound (b), an amide compound (c), and a thiophosphorous compound or a thiophosphoric acid ester compound (d), wherein the diurea compound (b) includes a compound represented by Formula (1) R 1 —NHCONH—R 2 —NHCONH—R 3  (1) wherein R 1  and R 3  represent an acyclic aliphatic hydrocarbon group having from 8 to 20 carbon atoms, and R 2  represents a diphenylmethane group.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a grease composition.

BACKGROUND OF THE INVENTION

Mechanical elements having a reciprocating sliding ball interposed therebetween include linear guides, ball screws, and constant velocity joints, and the environments in which they are used, are diverse. Rolling and sliding can occur simultaneously in the mechanical elements, and the lubrication environment can be harsh. Under these conditions, contact between the surfaces of rolling members can easily occur, and wear or seizure can occur when the contact is significant.

An extreme pressure agent is often added to a lubricant such as lubricating oil and grease in order to prevent wear and seizure and to protect mechanical elements. Well-known extreme pressure agents include sulfur-based extreme pressure agents, phosphorus-based extreme pressure agents, sulfur-phosphorus-based organic compounds, and molybdenum compounds. Among these extreme pressure agents, organic extreme pressure agents have become especially popular as they exhibit excellent extreme pressure performance, and they are currently widely used in lubricating oil compositions.

For example, JP200111481A discloses a grease composition for a sliding constant velocity joint comprising a urea thickener, molybdenum sulfide dialkyldithiocarbamate, molybdenum disulfide, a sulfur-phosphorus-based extreme pressure agent such as zinc dithiophosphate or thiophosphate, and a fatty acid amide to improve lubricity in portions prone to wear and likely to cause problems such as abnormal vibrations. According to this document, the occurrence of induced thrust force in a constant velocity joint causes problems such as reduced durability of the constant velocity joint, abnormal vibration of the vehicle, and a deterioration in riding comfort, but that use of the technique disclosed in this patent document reduces wear, suppresses vibration, and improves durability.

JP 2003321694A discloses a technique in which a grease composition contains a urea thickener and an organic sulfonate to prevent flaking from metal fatigue caused by thinning of an oil film despite attempts to thicken the oil film, and to extend flaking service life due to metal fatigue.

JP200382374A discloses a technique in which a rolling bearing grease composition contains a urea thickener and a benzotriazole and/or derivative to prevent flaking from metal fatigue caused by thinning of an oil film despite attempts to thicken the oil film, and to extend flaking service life.

JP2008239687A discloses a technique in which a bearing grease composition contains a urea thickener, an alkyl phosphorothioate compound, and an aliphatic amine

JP201725189A discloses a technique in which a grease composition contains a urea thickener, molybdenum dithiocarbamate, zinc dithiocarbamate, and zinc sulfonate to prevent metal-to-metal contact in lubrication even under high speed/high surface pressure conditions and to form and maintain an additive film that reduces friction.

The lubricants and grease compositions in JP200111481A, JP2003321694A, JP200382374, JP2008239687 and JP201725189A exhibit good wear resistance and film forming ability under specific conditions or for specific mechanical elements, but a composition able to stably maintain an overall balance between wear resistance and film forming ability during reciprocating sliding under various high loads has not been provided. In particular, the effects of reciprocating sliding on flaking under various high loads have not been studied and may be insufficient.

In view of this situation, it is an object of the present invention to maintain and improve the service life of mechanical parts even when rolling stops momentarily during reversal of reciprocal sliding, an oil film cannot be sufficiently generated, metal-on-metal contact occurs, and frictional wear tends to be excessive. It is also an object of the present invention to form a strong additive film, to stably maintain film that has already been formed even after repeated operation, and to provide stable lubricating properties. In other words, it is an object of the present invention to provide a grease composition that can be used to lubricate mechanical elements having a reciprocating sliding ball interposed therebetween and to maintain flaking resistance even under a high load.

SUMMARY OF THE INVENTION

As a result of extensive research conducted to achieve the objects mentioned above, the present inventors discovered that a grease composition containing an amide compound, a thiophosphorous acid compound or thiophosphoric acid ester compound, and a specific diurea compound could be used on mechanical elements having a reciprocating sliding ball interposed therebetween to improve flaking resistance. The present invention is a product of this discovery. Specifically, the present invention is the following.

Aspect (1) of the present invention is a grease composition comprising a base oil (a), a diurea compound (b), an amide compound (c), and a thiophosphorous compound or a thiophosphoric acid ester compound (d), wherein the diurea compound (b) includes a compound represented by Formula (1)

R₁—NHCONH—R₂—NHCONH—R₃  (1)

wherein, R₁ and R₃ represent an acyclic aliphatic hydrocarbon group having from 8 to 20 carbon atoms, and R₂ represents a diphenylmethane group.

Aspect (2) of the present invention is a grease composition according to aspect (1) of the present invention, wherein the diurea compound (b) includes a diurea compound (b) in which R₁ and R₃ in Formula 1 are either an acyclic aliphatic hydrocarbon group having from 8 to 12 carbon atoms or an acyclic aliphatic hydrocarbon group having from 14 to 20 carbon atoms.

Aspect (3) of the present invention is a grease composition according to aspect (1) or (2) of the present invention, further comprising a saturated or an unsaturated fatty acid having from 4 to 18 carbon atoms or a metal salt thereof (e).

Aspect (4) of the present invention is a grease composition according to any one of aspects (1) to (3) of the present invention, further comprising an amine compound (f) represented by Formula (2)

R₄—NH—R₅—NH₂  (2)

wherein R₄ represents a saturated or an unsaturated hydrocarbon group having from 5 to 18 carbon atoms, and R₅ represents a saturated or an unsaturated hydrocarbon group having from 2 to 3 carbon atoms.

Aspect (5) of the present invention is a grease composition according to any one of aspects (1) to (4) of the present invention, wherein the amide compound (c) includes an amide compound (c) represented by Formula (3) or Formula (4)

R₆—CO—NH₂  (3)

R₆—CO—NH—R₇—NH—CO—R₆  (4)

wherein R₆ represents a saturated or an unsaturated hydrocarbon group having from 15 to 17 carbon atoms, and R₇ represents a methylene group or an ethylene group.

Aspect (6) of the present invention is a grease composition according to any one of aspects (1) to (5) of the present invention, wherein the thiophosphorous compound includes a thiophosphorous compound represented by Formula (5), and the thiophosphoric acid ester compound includes a thiophosphoric acid ester compound represented by Formula (6)

(R₈S)₃P  (5)

(R₉O)₃PS  (6)

wherein R₈ represents a saturated or an unsaturated hydrocarbon group having from 8 to 18 carbon atoms or an aryl group having from 6 to 18 carbon atoms, and wherein R₉ represents a saturated or an unsaturated hydrocarbon group having from 8 to 18 carbon atoms or an aryl group having from 6 to 18 carbon atoms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an overview of a flaking resistance tester.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is able to provide a grease composition that can be used to lubricate mechanical elements having a reciprocating sliding ball interposed therebetween and maintain flaking resistance even under a high load in mechanical elements having a reciprocating sliding ball interposed therebetween.

In the present application, “hydrocarbon group” refers to a group of atoms obtained when some of the hydrogen atoms have been removed from a hydrocarbon.

When the name of a compound appears in the present application, the name includes all isomers of the compound.

In the present application, an amine compound that forms a diurea compound described below is referred to as a starting amine compound. A starting amine compound and amine compound (f) may be the same or different. When the amount of amine compound (f) is mentioned in the present specification, the amount does not include the starting amine compound.

A grease composition of the present invention comprises a base oil (a), a diurea compound (b), an amide compound (c), and a thiophosphorous compound or a thiophosphoric acid ester compound (d).

The diurea compound (b) in the present invention includes a compound represented by Formula (1)

R₁—NHCONH—R₂—NHCONH—R₃  (1)

wherein R₁ and R₃ represent an acyclic aliphatic hydrocarbon group having from 8 to 20 carbon atoms, and R₂ represents a represents a diphenylmethane group.

A diurea compound (b) in the present invention is generally produced by reacting an isocyanate with a primary amine (starting amine compound). It should be understood that the morphology of the thickener fibers in a diurea thickener depends on the combination of isocyanate and primary amine (starting amine compound), and that the flow characteristics of the resulting grease composition vary significantly.

It should be understood that an aliphatic urea grease using a diurea compound (b) in Formula 1 as a thickener can be a urea grease composed of an alicyclic amine and an aromatic amine or a urea grease consisting of a mixture of an aliphatic amine and an alicyclic amine and/or aromatic amine, and that these have different flow characteristics. It should also be understood that a grease using a diurea compound (b) in Formula 1 as a thickener tends to have excellent intervention properties at a lubrication interface and plays an important role in protecting mechanical elements. It should also be understood that a grease using a diurea compound (b) in Formula 1 as a thickener has good base oil solubility and intervenes at the lubrication interface along with the base oil, so that the different flow morphologies of the fibers interact with each other to provide good flow behavior and impart effective lubricity. It should also be understood that these effects are pronounced in an aliphatic urea grease containing an unsaturated aliphatic amine.

It should also be understood that a grease composition of the present invention containing a diurea compound (b), an amide compound (c), and a thiophosphite compound or thiophosphate ester compound (d) has a remarkable effect on improving anti-flaking performance as described below, and that the addition of a fatty acid or fatty acid salt and an amine compound (f) different from the starting amine compound used to form the diurea compound (b) has the effect of further improving the anti-flaking performance of mechanical elements having a reciprocating sliding ball interposed therebetween.

It should also be understood that this has the effect of thickening the lubricating film due to the improved supply of grease composition to the lubricating interface resulting from the excellent flow characteristics exhibited by the aliphatic diurea thickener in the fluid lubrication range in which the reciprocating sliding speed is high, and that in addition to the lubricating film of the diurea compound (b), the synergistic thickening effect with the urea grease due to the flow characteristics of the amide compound (c) and the fatty acid or fatty acid salt (e) as well as adsorption to metal surfaces further improves wear resistance. It should also be understood that, in the mixed lubrication region and in the boundary lubrication region where the oil film near the end point of the reciprocating motion approaches zero, the thiophosphite compound or thiophosphoric acid ester compound (d) and the amine compound (f) included in the grease composition abundantly supplied to the lubrication interface due to the excellent flow characteristics of the grease are adsorbed on the metal surfaces, and that the strong coating formed at the interface due to the tribochemical reaction exhibits good anti-flaking performance.

A grease composition of the present invention contains a base oil (a). There are no particular restrictions on the base oil (a) used in the present invention as long as the effects of the present invention are not impaired. The base oil (a) can be a mineral oil, a synthetic oil, an animal or a vegetable oil, or any mixture thereof. Specific examples are those in Groups 1 to 5 of the base oil categories of the American Petroleum Institute (API). The API base oil categories are a broad classification of base oil materials defined by the American Petroleum Institute in order to create guidelines for lubricating base oils.

There are no particular restrictions on the mineral oils used in the present invention. However, preferred examples include paraffin-based or naphthene-based mineral oils obtained by applying one or more refining means, such as solvent degassing, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, sulfuric acid washing and clay treatment, to a lubricating oil fraction obtained by atmospheric distillation and vacuum distillation of crude oil. These can be used alone or in combinations of two or more.

There are no particular restrictions on the synthetic oils used in the present invention. However, preferred examples include poly α-olefins (PAO) and hydrocarbon synthetic oils (oligomers). A PAO is an α-olefin homopolymer or copolymer. An α-olefin is a compound with a C—C double bond at the terminal, and specific examples include butene, butadiene, hexene, cyclohexene, methylcyclohexene, octene, nonene, decene, dodecene, tetradecene, hexadecene, octadecene, and eicosene. Examples of hydrocarbon synthetic oils (oligomers) include ethylene, propylene, and isobutene homopolymers or copolymers. These can be used alone or in combinations of two or more. These compounds may have any isomeric structure as long as they have a C—C double bond at the terminal, and may have a branched structure or a linear structure. These structural isomers and positional isomers with double bonds can be used in combinations of two or more. Among these olefins, a linear olefin having from 6 to 30 carbon atoms is preferred because the flash point is low when the number of carbon atoms is five or less, and the viscosity is high and the olefin impractical when the number of carbon atoms is 31 or higher.

In the present invention, a gas-to-liquid (GTL) base oil synthesized using the Fischer-Tropsch method for converting natural gas into liquid fuel can be used as the base oil (a). Compared to a mineral base oil refined from crude oil, a GTL base oil has a very low sulfur and aromatic content and a very high paraffin component ratio. As a result, it has excellent oxidative stability and very low evaporation loss, and is ideal for use as a base oil (a) in the present invention.

The grease composition of the present invention contains a diurea compound (b) represented by Formula (1)

R₁—NHCONH—R₂—NHCONH—R₃  (1)

wherein R₁ and R₃ represent an acyclic aliphatic hydrocarbon group having from 8 to 20 carbon atoms, and R₂ represents a diphenylmethane group.

R₁ and R₃ may be any acyclic aliphatic hydrocarbon group, and may be a linear or branched saturated or unsaturated aliphatic hydrocarbon group. R₁ and R₃ may have the same structure or different structures.

The diurea compound (b) in the present invention can be obtained using the reaction in Formula (7) below.

NCO—R₂—OCN+R₁—NH₂+R₃—NH₂→R₁—NHCONH—R₂—NHCONH—R₃  (7)

R₁ and R₃ are preferably an acyclic aliphatic hydrocarbon group having from 8 to 12 carbon atoms or an acyclic aliphatic hydrocarbon group having from 14 to 20 carbon atoms. More preferably, one of R₁ and R₃ is an acyclic aliphatic hydrocarbon group having from 8 to 12 carbon atoms and the other is an acyclic aliphatic hydrocarbon group having from 14 to 20 carbon atoms. When R₁ and R₃ have these structures, a grease composition with even better wear resistance and flaking resistance can be obtained.

The diurea compound (b) of the present invention can be used alone or in combinations of two or more.

The grease composition of the present invention contains an amide compound (c). There are no particular restrictions on the amide compound (c) used in the present invention as long as it does not impair the effects of the present invention. A preferred example of an amide compound (c) that can be used in the present invention is an aliphatic amide compound represented by Formula (3) below or an aliphatic bisamide compound represented by Formula (4) below. When the amide compound (c) has one of these structures, a grease composition with even better wear resistance and flaking resistance can be obtained.

R₆—CO—NH₂  (3)

R₆—CO—NH—R₇—NH—CO—R₆  (4)

In these formulas, R₆ represents a saturated or an unsaturated hydrocarbon group having from 15 to 17 carbon atoms and R₇ represents a methylene group or an ethylene group.

Specific examples of aliphatic amide compounds and aliphatic bisamide compounds include palmitic acid amide, palmitoleic acid amide, margaric acid amide, stearic acid amide, oleic acid amide, vaccenic acid amide, linoleic acid amide, linolenic acid amide, eleostearic acid amide, arachidic acid amide, eicosadienoic acid amide, mead acid amide, arachidonic acid amide, erucic acid amide, behenic acid amide, methylene bispalmitic acid amide, methylene bispalmitoleic acid amide, methylene bismargaric acid amide, methylene bisstearic acid amide, methylene bisoleic acid amide, methylene bisbacenoic acid amide, methylene bislinoleic acid amide, methylene bislinolenic acid amide, methylene bis-eleostearic acid amide, ethylene bispalmitic acid amide, ethylene bispalmitoleic acid amide, ethylene bismargalinamide, ethylene bisstearic acid amide, ethylene bisoleic acid amide, ethylene bisbacenoic acid amide, ethylene bislinoleic acid amide, ethylene bislinolenic acid amide, and ethylene bis-eleostearic acid amide. These can be used alone or in combinations of two or more.

The grease composition of the present invention contains a thiophosphorous acid compound or a thiophosphoric acid ester compound (d). There are no particular restrictions on the thiophosphorous acid compound or thiophosphoric acid ester compound (d) used in the present invention as long as the effects of the present invention are not impaired. A thiophosphorous acid compound may also be combined with a thiophosphoric acid ester compound.

The thiophosphorous compound or thiophosphoric acid ester compound (d) used in the present invention is preferably a thiophosphorous compound represented by Formula (5) below or a thiophosphoric acid ester compound represented by Formula (6) below. When the thiophosphorous compound or thiophosphoric acid ester compound has one of these structures, a grease composition with even better wear resistance and flaking resistance can be obtained.

(R₈S)₃P  (5)

R₈ represents a saturated or an unsaturated hydrocarbon group having from 8 to 18 carbon atoms or an aryl group having from 6 to 18 carbon atoms.

(R₉O)₃PS  (6)

R₉ represents a saturated or an unsaturated hydrocarbon group having from 8 to 18 carbon atoms or an aryl group having from 6 to 18 carbon atoms.

Specific examples of thiophosphorous acid compounds and thiophosphoric acid ester compounds (d) include alkyl thiophosphites such as trilauryl trithiophosphite and aromatic thiophosphates such as triphenyl phosphorothioate. When an alkyl thiophosphite is used, a grease composition with even better wear resistance and flaking resistance can be obtained. These can be used alone or in combinations of two or more.

The grease composition of the present invention can also contain any of the following components. When a grease composition of the present invention contains a fatty acid or a metal salt thereof (e) or an amine compound (f), better wear resistance and flaking resistance can be obtained. When a grease composition of the present invention contains a fatty acid or a metal salt thereof (e) and an amine compound (f), even better wear resistance and flaking resistance can be obtained.

The grease composition of the present invention can contain a fatty acid or a metal salt thereof (e). There are no particular restrictions on the fatty acids or metal salt thereof (e) used in the present invention as long as they do not impair the effects of the present invention. A fatty acid or metal salt thereof used in the present invention is preferably a saturated or an unsaturated fatty acid having from 4 to 18 carbon atoms or a metal salt thereof. When a grease composition of the present invention contains a fatty acid or a metal salt thereof (e), even better wear resistance and flaking resistance can be obtained.

Specific examples of fatty acids include butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, capric acid, lauric acid, myristic acid, pendadecyl acid, palmitic acid, margaric acid, stearic acid, crotonic acid, myristoleic acid, palmitoleic acid, sapienoic acid, oleic acid, linoleic acid, linolenic acid, pinolenic acid, eleostearic acid, stearidonic acid, and eicosapentaenoic acid. These can be used alone or in combinations of two or more. Because unsaturated fatty acids are more easily adsorbed on a metal surface than saturated fatty acids, they are preferred from the standpoint of obtaining a grease composition with excellent wear resistance and flaking resistance. As for the carbon number, a larger number of carbon atoms is more preferable. Oleic acid is an example of such a fatty acid.

There are no particular restrictions on the metal element used to form a salt with these fatty acids as long as the effects of the present invention are not impaired. Specific examples of metal elements include alkali metals such as lithium, sodium, potassium, rubidium and cesium; beryllium; magnesium; alkaline earth metals such as calcium, strontium and barium; aluminum; and zinc. These can be used alone or in combinations of two or more. Among these, calcium and aluminum salts are preferred from the standpoint of obtaining a grease composition with excellent wear resistance and flaking resistance.

The grease composition of the present invention can contain an amine compound (f). There are no restrictions on the amine compound (f) used in the present invention as long as the effects of the present invention are not impaired. The amine compound (f) used in the present invention is preferably an amine compound represented by Formula 2 below. When a grease composition of the present invention contains such an amine compound, even better wear resistance and flaking resistance can be obtained.

R₄—NH—R₅—NH₂  (2)

R₄ represents a saturated or an unsaturated hydrocarbon group having from 5 to 18 carbon atoms, and R₅ represents a saturated or an unsaturated hydrocarbon group having from 2 to 3 carbon atoms.

Specific examples of amine compounds (f) include N-coconut alkyl-1,2-ethylenediamine, N-beef tallow alkyl-1,2-ethylenediamine, N-hardened beef tallow alkyl-1,2-ethylenediamine, N-coconut alkyl-1,3-propanediamine, N-beef tallow alkyl-1,3-propanediamine, N-hardened beef tallow alkyl-1,3-propanediamine, N-coconut alkyl-1,3-propylenediamine, N-beef tallow alkyl-1,3-propylenediamine, N-hardened beef tallow alkyl-1,3-propylenediamine, N-coconut alkyl-1,4-butylenediamine, N-beef tallow alkyl-1,4-butylenediamine, and N-hardened beef tallow alkyl-1,4-butylenediamine. These can be used alone or in combinations of two or more. Among these, N-beef tallow alkyl-1,3-propanediamine is preferred from the standpoint of obtaining a grease composition with excellent wear resistance and flaking resistance.

The grease composition of the present invention can include a thickener other than a urea compound (other thickener) in addition to the (urea) thickeners mentioned above. Examples of other thickeners include tricalcium phosphate, alkali metal soaps, alkali metal composite soaps, alkaline earth metal soaps, alkaline earth metal composite soaps, alkali metal sulfonates, alkaline earth metal sulfonates, other metal soaps, terephthalamate metal salts, monourea, polyureas other than triurea monourethane, diurea or tetraurea, clays, silicas (silicon oxide) such as silica airgel, and fluororesins such as polytetrafluoroethylene. These can be used alone or in combinations of two or more. In addition to these thickeners, any substance that can impart a viscous effect to a liquid substance can be used. When any of the fatty acids or metal salts thereof (e) mentioned above is used, the fatty acid or metal salt thereof (e) can double as a thickener. When a fatty acid or metal salt thereof (e) doubles as a thickener, the amount used can differ from the amount of fatty acid or metal salt thereof (e) mentioned above.

The grease composition of the present invention can include additives such as antioxidants, rust inhibitors, oiliness agents, extreme pressure agents, antiwear agents, solid lubricants, metal deactivators, polymers, non-metal detergents, colorants, and water repellents as long as they do not impair the present invention. These can be used alone or in combinations of two or more.

Examples of antioxidants include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butylparacresol, p,p′-dioctyldiphenylamine, N-phenyl-α-naphthylamine, and phenothiazine.

Examples of rust inhibitors include paraffin oxides, carboxylic acid metal salts, sulfonic acid metal salts, carboxylic acid esters, sulfonic acid esters, salicylates, succinates, sorbitan esters, and various amine salts.

Examples of oiliness agents, extreme pressure agents and antiwear agents include zinc sulfide dialkyl dithiophosphates, zinc sulfide diallyl dithiophosphates, zinc sulfide dialkyl dithiocarbamates, zinc sulfurized diallyl dithiocarbamates, molybdenum sulfide dialkyl dithiophosphates, molybdenum sulfide diallyl dithiophosphates, molybdenum sulfide dialkyl dithiocarbamates, molybdenum sulfide diallyl dithiocarbamates, organic molybdenum complexes, olefin sulfides, triphenyl phosphite, triphenyl phosphorothionate, tricresin phosphite, other phosphates, and sulfurized oils and fats.

Examples of solid lubricants include molybdenum disulfide, graphite, boron nitride, melamine cyanurate, PTFE (polytetrafluoroethylene), tungsten disulfide, and fluorinated graphite. Examples of metal deactivator include N,N′-disalicylidene-1,2-diaminopropane, benzotriazole, benzimidazole, benzothiazole, and thiadiazole. Examples of polymers include polybutene, polyisobutene, polyisobutylene, polyisoprene, and polymethacrylate.

An example of a non-metallic detergent is succinimide.

There are no particular restrictions on the method used to produce a grease composition of the present invention. However, a grease composition of the present invention can be produced by weighing each raw material and mixing them together using any well-known method. As for the amounts of optional components added, the amounts mentioned above can be used if necessary.

The amount of base oil (a) used per 100% by mass overall grease composition is preferably 70 to 98% by mass, more preferably 75 to 97% by mass, and even more preferably 80 to 95% by mass.

The amount of diurea compound (b) in the present invention used per 100% by mass overall grease composition is preferably 1 to 25% by mass, more preferably 3 to 20% by mass, and even more preferably 5 to 15% by mass. When a thickener other than the diurea compound (b) is added, the total amount of diurea compound (b) and thickener other than the diurea compound (b) used per 100% by mass overall grease composition is preferably 2 to 50% by mass, more preferably 4 to 40% by mass, and even more preferably 6 to 30% by mass. When the amount of diurea compound (b) is within this range, the grease composition has the right hardness for a grease, does not flow away from the lubrication sites, has excellent intervening properties on lubricated interfaces, and achieves the desired lubrication performance.

The amount of amide compound (c) in the present invention used per 100% by mass overall grease composition is preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass, and even more preferably 0.3 to 3% by mass.

The amount of thiophosphorous acid compound or thiophosphoric acid ester compound (d) in the present invention used per 100% by mass overall grease composition is preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass, and even more preferably 0.3 to 3% by mass.

The amount of fatty acid or metal salt thereof (e) in the present invention used per 100% by mass overall grease composition is preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass, and even more preferably 0.3 to 3% by mass.

The amount of amine compound (f) in the present invention used per 100% by mass overall grease composition is preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass, and even more preferably 0.3 to 3% by mass.

The amount of any additional additive used per 100 parts by mass of overall grease composition is preferably 0.1 to 20 parts by mass.

The grease composition of the present invention has a consistency in a range from no. 2 to no. 0 (265 to 385), preferably from no. 4 to no. 00 (175 to 430), more preferably from no. 3 to no. 0 (220 to 385), and even more preferably from no. 2 to no. 1 (265 to 340). Consistency indicates the physical hardness of a grease. The method used to measure consistency here is in accordance with the “grease consistency testing method” in JIS K2220 7.

Dropping Point is not relevant to the performance of a grease composition of the present invention, but is preferably 180° C. or higher as an indicator that a urea grease thickener structure has reached the original binding. As the temperature rises, the dropping point is the temperature at which a viscous grease loses its thickener structure. The method used to measure dropping point is the “grease dropping point testing method” in JIS K2220 8.

The grease composition of the present invention can naturally be used in machinery, bearings, gears, and ball screws where excellent performance can be exhibited as grease lubrication even in harsh environments. It is suitable for lubricating various automotive components, including components surrounding an engine such as water pumps, cooling fan motors, starters, alternators and actuators, as well as propeller shafts, constant velocity joints (CVJ), powertrain components such as wheel bearings and clutches, electric power steering (EPS) components, electric power window components, braking devices, ball joints, door hinges, handle components, and brake expanders. A grease composition of the present invention is preferably used on shafts and fittings that slide back and forth in construction machinery such as power shovels, bulldozers and mobile cranes, in the steel industry, in the paper industry, in forestry machinery, in agricultural machines, in chemical plant, in power generating equipment, and in train cars. Other applications include screw joints for seamless pipes and outboard motor bearings. A grease composition of the present invention is especially suitable for these applications.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an overview of a flaking resistance tester. The following parts are marked as indicated below:

-   1: Motor -   2: Rotation axis -   3: Crank arm (1) -   4: Strain gauge -   5: Crank bent portion -   6: Crank arm (2) -   7: Fitting retaining nut -   8: Key material -   9: Cone fitting portion -   10: Nut -   11: Collar -   12: Bearing retaining block -   13: Test rolling bearing -   14: Bearing unit -   15: Load control device -   16: Auxiliary rolling bearing -   17: Swing shaft

EXAMPLES

The following is a detailed description of the invention with reference to examples and comparative examples. Note, however, that the present invention is not limited in any way to these examples.

Raw Material Components

The following raw material components were used in the examples and comparative examples.

Base Oils (a)

-   -   Base Oil A: A mineral oil with a kinematic viscosity at 40° C.         of 99.05 mm²/s and a kinematic viscosity at 100° C. of 11.13         mm²/s.     -   Base Oil B: A mineral oil with a kinematic viscosity at 40° C.         of 480.2 mm²/s and a kinematic viscosity at 100° C. of 31.56         mm²/s.     -   Base Oil C: A highly refined oil with a kinematic viscosity at         40° C. of 43.88 mm²/s, a kinematic viscosity at 100° C. of 7.774         mm²/s, a viscosity index of 146, % CA of 1 or less, % CN of         11.9, and % CP of 85 or more.     -   Base Oil D: A poly α-olefin oil with a kinematic viscosity at         40° C. of 396.5.3 mm²/s and a kinematic viscosity at 100° C. of         39.99 mm²/s.     -   Base Oil E: An alkyl diphenyl ether oil with a kinematic         viscosity at 40° C. of 102.2 mm²/s and a kinematic viscosity at         100° C. of 12.64 mm²/s.

Diurea Compounds (b)

Diurea compounds (b) were prepared by reacting the following raw materials using the production method described below.

-   -   Diurea Compound A:         Diphenylmethane-4,4′-diisocyanate (MDI)

Octylamine Oleylamine

-   -   Diurea Compound B:         Diphenylmethane-4,4′-diisocyanate (MDI)

Octylamine Amide Compounds (c)

-   -   Amide Compound A: Oleic acid amide (Armoslip CP from Lion         Specialty Chemicals)

Thiophosphorous Acid Compounds and Thiophosphoric Acid Ester Compounds (d)

-   -   Thiophosphorous Acid Compound A: Trilauryltrithiophosphite         (JPS-312 from Johoku Chemical)     -   Thiophosphoric Acid Ester Compound A:         Triphenylphosphorothioate (Irgalube TPPT from BASF)

Fatty Acids or Metal Salts Thereof (e)

-   -   Fatty Acid A: Oleic acid (NAA-35 from NOF)     -   Fatty Acid Metal Salt A: Calcium stearate (Calcium Stearate GP         from NOF)     -   Fatty Acid Metal Salt B: Aluminum stearate (Aluminum Stearate         300 from NOF)

Amine Compounds (f)

-   -   Amine Compound A: N-beef tallow alkyl-1,3-propanediamine         (Lipomin DA-T from Lion Specialty Chemicals)

Example 1

After heating a base oil and MDI in a vessel to dissolve the contents, a raw material mixture prepared by dissolving and mixing together octylamine, oleylamine and a base oil was added to the vessel and reacted to synthesize diurea compound A. The mixture was then heated to 170° C. while stirring, and this temperature was maintained for about 30 minutes to complete the reaction. Afterward, the mixture was rapidly cooled, various additives were added during the cooling process at the compounding ratios shown in Table 1, and the resulting mixture was mixed while stirring, cooled to 80° C., and passed through a homogenizer to obtain a grease.

Examples 2-18, Comparative Examples 1-5

Grease compositions were prepared in the same manner as Example 1 except that the raw materials blended together were those shown in Tables 1 to 4. Diurea Compound B was prepared by changing the raw materials in Diurea Compound A to those listed above.

Evaluation of Grease Compositions

The following measurements and tests were performed in order to compare the properties and performance of the examples and comparative examples.

The worked penetration and unworked penetration of the grease compositions in the examples and comparative examples were measured in accordance with the “grease consistency testing method” in JIS K2220 7. The results are shown in Tables 1 to 4.

The dropping point of the grease compositions in the examples and comparative examples was measured in accordance with the “grease dropping point testing method” in JIS K2220 8. The results are shown in Tables 1 to 4.

The wear resistance and flaking resistance of the grease compositions in the examples and comparative examples were evaluated in a bearing flaking and wear test. The results are shown in Tables 1 to 4. The following is a description of the evaluation method. FIG. 1 is a diagram showing an overview of a bearing flaking and wear tester. The weight of a clean test rolling bearing (no. 7205 angular contact ball bearing) was measured in advance, and 3 g of grease composition was applied to the bearing and loaded in the bearing flaking and wear tester. The nut for the swing shaft was then secured with tightening torque of 600 kg-m, and a thrust load was applied to the shaft by the tightening torque. Next, a hydraulic piston was used to apply a radial load of 1.0 ton per bearing. The motor was started and the swing shaft was reciprocated at 1.7 Hz. After performing the swinging operation for 20 hours, the bearing was removed from the device and washed with a solvent such as n-hexane to thoroughly remove the grease composition. The weight of the clean bearing after the test was measured, and the weight difference relative to the weight of the bearing before the test was calculated to obtain the amount of bearing wear. The amount of bearing wear after the test and area of the sliding surfaces of the inner ring and the outer ring experiencing flaking were measured to evaluate whether the grease composition passed or failed. The pass/fail decision was based on the area in which flaking occurred. When the area was less than 50 mm², the grease composition passed. When the area was greater, the grease composition failed. The area experiencing flaking was determined by observing and specifying the portions in which flaking occurred under a digital microscope (VHX-6000 from Keyence), and then the area was measured.

Testing Conditions

Test bearing: no. 7205 (Angular ball bearing) Amount of grease: 3.0 g

Oscillation: 1.7 Hz

Thrust load: 600 Kg·m Radial load: 1.0 ton

Temperature: 25° C.

Time: 20 hours

Evaluation Results

The worked penetration, dropping point, and bearing flaking and wear tests were conducted in accordance with the methods described above. The properties of each grease are shown in Tables 1 to 4. The grease compositions in the examples had a consistency from no. 0 to no. 2, and the grease compositions of the comparative examples had a consistency from no. 2 to no. 2.5. The dropping points of the grease compositions in both the examples and the comparative examples at 240° C. or higher were comparable to those of urea greases. The results of the bearing flaking and wear test were the most important for the present invention, and all of the grease compositions of the present invention passed with an amount of bearing wear of less than 150 mg and a total flaking area of less than 50 mm². In the case of the grease compositions in the comparative examples, the amount of bearing wear after the bearing flaking and wear test was significant, and the total flaking area on the sliding surfaces of the inner ring and the outer ring exceeded 50 mm², which means they failed the test.

TABLE 1 Examples 1 2 3 4 5 6 7 Base Oil mass % Lubricating Oil A 90.80 90.80 47.00 27.15 24.30 24.30 91.20 Lubricating Oil B 47.00 Lubricating Oil C 27.15 24.30 24.30 Lubricating Oil D 36.20 24.30 24.30 Lubricating Oil E 17.10 17.10 Diurea Compound mass % Diurea Compound A 8.2 8.2 5 8.5 9 8.2 Diurea Compound B 9 Additives mass % Amide Compound A 0.5 0.5 0.5 0.5 0.5 0.5 0.3 Thiophosphorous 0.5 0.5 0.5 0.3 Acid Compound A Thiophosphoric Acid 0.5 0.5 0.5 Ester Compound A Fatty Acid A Fatty Acid Salt A Fatty Acid Salt B Amine Compound A Additive Total mass % 1.0 1.0 1.0 1.0 1.0 1.0 0.6 Compound Total mass % 100 100 100 100 100 100 100 Base Oil Properties KV 40° C. mm²/sec 99.05 99.05 212.49 134.90 115.89 115.89 99.05 KV 100° C. mm²/sec 11.13 111.3 18.39 16.59 14.56 14.56 11.13 Viscosity Index 97 97 96 132 128 128 97 Grease Properties Consistency unmixed 265 268 357 283 279 276 266 Consistency mixed 270 273 362 285 289 286 269 Dropping Point ° C. >270 >270 >270 >270 >270 >270 >270 Bearing Wear After 105.0 123.1 102.6 87.9 90.8 106.7 142.8 Test mg Braking Evaluation Pass Pass Pass Pass Pass Pass Pass

TABLE 2 Examples 8 9 10 11 12 13 14 Base Oil mass % Lubricating Oil A 90.80 90.80 90.80 91.20 90.80 90.80 90.80 Lubricating Oil B Lubricating Oil C Lubricating Oil D Lubricating Oil E Diurea Compound mass % Diurea Compound A 8.2 8.2 8.2 8.2 8.2 8.2 8.2 Diurea Compound B Additives mass % Amide Compound A 0.3 0.3 0.3 0.3 0.3 0.3 0.5 Thiophosphorous 0.3 0.3 0.3 0.25 Acid Compound A Thiophosphoric Acid 0.3 0.3 0.3 0.25 Ester Compound A Fatty Acid A 0.4 0.4 Fatty Acid Salt A 0.4 Fatty Acid Salt B 0.4 Amine Compound A 0.4 Additive Total mass % 1.0 1.0 1.0 0.6 1.0 1.0 1.0 Compound Total mass % 100 100 100 100 100 100 100 Base Oil Properties KV 40° C. mm²/sec 99.05 99.05 99.05 99.05 99.05 99.05 99.05 KV 100° C. mm²/sec 11.13 11.13 11.13 11.13 11.13 11.13 11.13 Viscosity Index 97 97 97 97 97 97 97 Grease Properties Consistency unmixed 265 268 270 269 265 274 271 Consistency mixed 270 273 278 276 271 283 278 Dropping Point ° C. >270 >270 >270 >270 >270 257 >270 Bearing Wear After 132.9 129.4 131.0 149.0 139.2 102.0 125.9 Test mg Braking Evaluation Pass Pass Pass Pass Pass Pass Pass

TABLE 3 Examples 15 16 17 18 Base Oil mass % Lubricating Oil A 24.46 24.35 24.30 88.00 Lubricating Oil B Lubricating Oil C 24.46 24.35 24.30 Lubricating Oil D 24.46 24.35 24.30 Lubricating Oil E 17.21 17.14 17.10 Diurea Compound mass % Diurea Compound A Diurea Compound B 9 9 9 9 Additives mass % Amide Compound A 0.2 0.2 0.2 1.5 Thiophosphorous 0.2 0.2 0.2 Acid Compound A Thiophosphoric Acid 1.5 Ester Compound A Fatty Acid A 0.2 0.2 Fatty Acid Salt A 0.2 0.2 Fatty Acid Salt B Amine Compound A 0.2 Additive Total mass % 0.4 0.8 1.0 3.0 Compound Total mass % 100 100 100 100 Base Oil Properties KV 40° C. mm²/sec 115.89 115.89 115.89 99.05 KV 100° C. mm²/sec 14.56 14.56 14.56 11.13 Viscosity Index 128 128 128 97 Grease Properties Consistency unmixed 276 277 284 289 Consistency mixed 285 283 293 295 Dropping Point ° C. >270 >270 247 >270 Bearing Wear After 131.2 125.0 79.5 95.6 Test mg Braking Evaluation Pass Pass Pass Pass

TABLE 4 Comparative Examples 1 2 3 4 5 Base Oil mass % Lubricating Oil A 91.80 91.30 91.30 91.30 90.80 Lubricating Oil B Lubricating Oil C Lubricating Oil D Lubricating Oil E Diurea Compound mass % Diurea Compound A 8.2 8.2 8.2 8.2 8.2 Diurea Compound B Additives mass % Amide Compound A 0.5 Thiophosphorous 0.5 0.5 Acid Compound A Thiophosphoric Acid Ester Compound A Fatty Acid A Fatty Acid Salt A 0.5 Fatty Acid Salt B Amine Compound A 0.5 Additive Total mass % 0.0 0.5 0.5 0.5 1.0 Compound Total mass % 100 100 100 100 100 Base Oil Properties KV 40° C. mm²/sec 99.05 99.05 99.05 99.05 99.05 KV 100° C. mm²/sec 11.13 11.13 11.13 11.13 11.13 Viscosity Index 97 97 97 97 97 Grease Properties Consistency unmixed 255 257 256 265 272 Consistency mixed 266 268 266 268 279 Dropping Point ° C. >270 >270 >270 >270 253 Bearing Wear After >250 193.5 198.8 189.9 188.6 Test mg Braking Evaluation Fail Fail Fail Fail Fail 

We claim:
 1. A grease composition comprising a base oil (a), a diurea compound (b), an amide compound (c), and a thiophosphorous compound or a thiophosphoric acid ester compound (d), wherein the diurea compound (b) includes a compound represented by Formula (1) R₁—NHCONH—R₂—NHCONH—R₃  (1) wherein R₁ and R₃ represent an acyclic aliphatic hydrocarbon group having from 8 to 20 carbon atoms, and R₂ represents a diphenylmethane group.
 2. A grease composition according to claim 1, wherein the diurea compound (b) includes a diurea compound (b) in which R₁ and R₃ in Formula 1 are either an acyclic aliphatic hydrocarbon group having from 8 to 12 carbon atoms or an acyclic aliphatic hydrocarbon group having from 14 to 20 carbon atoms.
 3. A grease composition according to claim 1, further comprising a saturated or an unsaturated fatty acid having from 4 to 18 carbon atoms or a metal salt thereof (e).
 4. A grease composition according to claim 1, further comprising an amine compound (f) represented by Formula (2) R₄—NH—R₅—NH₂  (2) wherein R₄ represents a saturated or an unsaturated hydrocarbon group having from 5 to 18 carbon atoms, and R₅ represents a saturated or an unsaturated hydrocarbon group having from 2 to 3 carbon atoms.
 5. A grease composition according to claim 1, wherein the amide compound (c) includes an amide compound (c) represented by Formula (3) or Formula (4) R₆—CO—NH₂  (3) R₆—CO—NH—R₇—NH—CO—R₆  (4) wherein R₆ represents a saturated or an unsaturated hydrocarbon group having from 15 to 17 carbon atoms, and R₇ represents a methylene group or an ethylene group.
 6. A grease composition according to claim 1, wherein the thiophosphorous compound includes a thiophosphorous compound represented by Formula (5), and the thiophosphoric acid ester compound includes a thiophosphoric acid ester compound represented by Formula (6) (R₈S)₃P  (5) (R₉O)₃PS  (6) wherein R₈ represents a saturated or an unsaturated hydrocarbon group having from 8 to 18 carbon atoms or an aryl group having from 6 to 18 carbon atoms and wherein R₉ represents a saturated or an unsaturated hydrocarbon group having from 8 to 18 carbon atoms or an aryl group having from 6 to 18 carbon atoms. 